参数资料
型号: L64781
厂商: LSI CORP
元件分类: 消费家电
英文描述: SPECIALTY CONSUMER CIRCUIT, PQFP100
封装: PLASTIC, QFP-100
文件页数: 91/164页
文件大小: 2003K
代理商: L64781
2-12
Architectural Overview
2.9.2 Digital Frequency Synchronization
The digital frequency synchronization block uses digital signal processing
(DSP) to correct for tolerance in the frequency of the local oscillator in
the tuner. The DSP shifts the frequency of the complex baseband signal
so that its center frequency is zero. The block takes the sequence of
complex numbers from the output of the FFT block and produces a
numerical control signal. It also takes the sequence of complex numbers
from the real-to-complex conversion block and applies the frequency shift
to those numbers according to the numerical control signal. Then, it
passes the data on to the FFT block.
2.9.3 Automatic Frequency Control (AFC) Loop Gain
In digital AFC mode, the optimal AFC_SENSITIVITY is 110:
Equation 2.9
In analog AFC mode, the optimal AFC_SENSITIVITY is dened as:
Equation 2.10
2.9.4
AFC_INIT_FREQ Register Denition
In AFC digital loop mode, the
AFC_INIT_FREQ register is dened as a
two’s-complement, 24-bit register and has the following meaning:
Equation 2.11
where
W0 is the central frequency of the VCXO.
In AFC analog loop mode, the
AFC_INIT_FREQ register is dened as a
two’s complement, 24-bit register and has the following meaning:
Equation 2.12
where
W0 is the central frequency of the VCXO.
K
SENS
1.56
2
×10
K
SENS
74.4
K
VCXO
--------------------
=
W
i
W
0
143
10
3
×
2
23
-------------------------
AFC INIT FREQ
×
+
=
W
i
W
0
3.3
K
vcxo
2
20
------------------------
AFC INIT FREQ
×
+
=
l64781.book Page 12 Friday, January 19, 2001 1:28 PM
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